As an information display device substitutable for liquid crystal display (LCD), information display devices with the use of technology such as an electrophoresis method, an electro-chromic method, a thermal method, dichroic-particles-rotary method are proposed.
As for these information display devices, it is conceivable as inexpensive visual display device of the next generation from a merit having wide field of vision close to normal printed matter, having smaller consumption with LCD, or having a memory function, and spreading out to a display for portable device and an electronic paper is expected. Recently, electrophoresis method is proposed that microencapsulate dispersion liquid made up with dispersion particles and coloration solution and dispose the liquid between faced substrates, and also it is expected.
However, in the electrophoresis method, there is a problem that a response rate is slow by the reason of viscosity resistance because the particles migrate among the electrophoresis solution. Further, there is a problem of lacking imaging repetition stability, because particles with high specific gravity of titanium oxide is scattered within solution of low specific gravity, it is easy to subside, difficult to maintain a stability of dispersion state. Even in the case of microencapsulating, cell size is diminished to a microcapsule level in order to make it hard to appear, however, an essential problem was not overcome at all.
Besides the electrophoresis method using behavior in the solution, recently, a method wherein electro-conductive particles and a charge transport layer are installed in a part of the substrate without using solution is proposed. [The Imaging Society of Japan “Japan Hardcopy '99” (Jul. 21-23, 1999) Transaction Pages 249-252] However, the structure becomes complicated because the charge transport layer and further a charge generation layer are to be arranged. In addition, it is difficult to constantly dissipate charges from the electro-conductive particles, and thus there is a drawback on the lack of stability.
As one method for overcoming the various problems mentioned above, an information display device comprising an information display panel is known, in which cells are formed in an isolated manner from one another by partition walls between a front substrate and a rear substrate and the particles or the liquid powders are sealed in the cells, and, in which the particles or the liquid powders, to which an electrostatic field is applied, are made to move by means of Coulomb's force and so on so as to display information such as an image.
In the information display device mentioned above, particles including white color particles and black color particles or colored particles having the other color are normally utilized. These particles are manufactured as crushed particles having an average particle diameter of for example 9 μm by melting and mixing resins, pigments so as to obtain a mixture and cruching the thus obtained mixture. In this case, if a white color reflectance of the white color particles is not sufficiently high such as 40% or more, there is a drawback such that a contrast of a display image is not obtained. Moreover, when the particles are sealed between the substrates, there is also a drawback such that the particles are fused and bonded to the substrate, if a heat resistance of the particles is not over a heat hardening temperature of adhesives such as over 120° C. As is well known in the art, in the particles using PP (polypropylene resin) or PBT (polybutylene terephthalate resin) as a resin, it is difficult to have both properties of contrast and heat resistance.